External Data can be easily import into Salesforce. Salesforce Offers Two main methods for Managing data.

Data Loader.

Data Import Wizard.

With both the data import methods,the number of records depends on your permissions, type of data you are importing and overall data storage limits of your organization.The types of objects you can import depends on your edition.
In General you can use Data Import wizard if you need to load less than 50,000 records else you can use Data Loader if u need to load 50,000 to Five million records.
Data Loader:-Data loader is a application for the bulk import and export of data.It is used to insert, update, delete or export salesforce records.When data is import from external source to salesforce, Data loader reads, extract, and load data from comma -seperated values(CSV)files.When Exporting Data, it outputs CSV files.

Every object has a standard field called id. There is no need to define an explicit primary key in custom objects. The standard id field can be used as primary key.

The id is alphanumeric. id can be either 18 digit case-insensitive or 15 digit case-sensitive.

The first three characters of the id identify the object. Ids can be identified in three ways .

The id displayed by a report is the 15-digit case-sensitive id. The ids returned by web services api are 18-digit id. For updates web service accept both the 15-digit and 18-digit ids.

15-digit id can be converted to 18-digit id and vice-versa.

There are two types of Data Loader logs:

sd1.log

sd1_out.log

When loading data into a salesforce application dependencies between objects determine the order in which objects are loaded. If there is a one-to-many relationship between A and B, the data for A should be loaded before the data for B.

Data Management is an ongoing process to keep data in your application up-to-date, accurate and clean whereas Data Migration is one time task.

External ids option can be specified on custom fields for fields of type text, number or email. This creates custom index in database. A maximum of three fields can be set as external ids. Specifying a field as external ids, leads to improved reporting and SOQL performance. External ids prevent duplicate entries when exporting data. Both upsert and external ids are used for migration and integration of data.

If "Modifiable System Field" configuration is enabled, then system fields (like creation date) can be set to any value during initial data load. These values can however not be updated after the initial upload. These fields are accessible through the API. These are backward compatible with all SOAP based APIs available for all custom objects. These are Read only fields.

Salesforce determines an operation Upsert. Upsert stands for update + insert. When an upsert is performed, if a record exists it gets updated. If the record does not exist, it gets inserted. This is useful in large data uploads, and if the connectivity is not stable. Matching of record can be performed on the basis of Salesforce id or External id. When performing an upsert, only single external id field is used.

Import wizard are available via the standard Salesforce application using easy to use interface and do not require programming. Import wizard can be used to load up to 50,000 records. Import wizard can be used for de-duplication of data. Import wizard can be used to import accounts, contacts, leads, solutions and custom objects.

Web Services API based tools can load more than 50,000 records and can support all object types. It also allows developers to schedule regular data loads. These support nightly feeds. APIs can delete multiple objects at the same time.

Data Loader is an API based product by Salesforce. It can be run from command-line. It can generate and import from csv (Comma Separated values) files. It supports custom relations imports using upserts. It also support loading from JDBC.

Data Loader can be installed on a desktop from the Salesforce Data Management menu. Operations supported by data loader are -

Extract

Upsert

Insert

Delete

Update

Command-line version of data-loader supports regular scheduling of loads.

Mass Transfer Tool is used to transfer multiple objects data from one user to another. User should have the following permissions:

Transfer record permission

Edit permissions

The tool can be used to change the ownership of the record.

Data Import Wizard:-Data Import Wizard is a tool which is easily accesible through Setup menu.Data import wizard lets you import data in common standard objects such as Leads,Contact,Account as well as in custom objects.It can importupto 50,000 records at a time.
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